Study On The Sea-echo Doppler Spectrum Of The Over-the-horizon Radar

The skywave Over-the-Horizon Radar (OTHR) is a special type of radar whichoperates in high frequency band (3-30MHz) and employs the ionosphere to reflectsignal to detect target from the top down. OTHR has some native advantages, such asthe capability of detecting low-flying target and stealth target, avoiding the attack ofanti-radiation missile, as well as providing wide area surveillance with longer earlywarning time than some other common radar. Therefore, OTHR plays a more and moreimportant role in modern air defense system and has potential significant contribution tomilitary applications. The target above sea can be detected and information of sea statecan be obtained by employing OTHR in illuminating sea and analyzing Dopplerspectrum of the sea echo．The main work is as follows:Based on the ocean scattering intensity formula proposed by Barrick，the oceanclutter spectrum is simulated．The characteristics of sea clutter distribution and itsdependence on parameter of sea state are deduced.The dependence of the frist-order sea clutter backscattering coefficient model, thechange discipline of the frist-order sea clutter backscattering along with the affection ofparameters of OTHR and its range of OTHR frist-order sea clutter backscatteringcoefficient and also the changing law on the whole can be gained.The relationship between the first-order Doppler of HF radar and the wind directionover the sea surface is discussed, a new method for predicting wind direction isproposed with considering the combination of neural network and the method of thebeam sampling according to the relationship. The validity and feasibility for this newmethod are verifited using the simulated data.The mechanism of the spreading domain of the sea clutter in shipbome OTHR isdiscussed, the spread frist-order sea cluuter is forcasted and eliminated by BP neuralnetwork due to the chaos propertity of sea clutter, and the azimuth information of thesignals is obtained by the MUSIC algorithm.